ranging

If you're driving in the country and have to stop the car to let a bunch of cows slowly cross the road, you'll be sitting there for a while admiring a herd of ranging, or freely wandering, cattle.

When ranging is used as an adjective, it can describe anything that wanders or varies or moves freely, from chickens to a bookmobile to your own thoughts. It can also be a verb, and in that case it's more likely to mean "varying." You could say, for example, that the ages of the people who show up at your family reunion are ranging from two and a half to ninety-seven.